1. Field of the Invention
The present invention relates to a method for operating a number of control units, and also relates to a central control unit and a system having a number of control units.
2. Description of Related Art
Various monitoring functions, which are cyclically executed even in the quiescent state of the vehicle, are implemented in control units of motor vehicles. Cycle times for implementing the functions are defined by a system function, such as by the so-called heartbeat for monitoring a control line between a theft alarm system and a siren, for example, or else by the cyclical monitoring of a battery state with the aid of an electronic battery sensor. For this purpose a control unit of a vehicle automatically switches between a function mode having increased current consumption and a quiescent mode during which a quiescent current is withdrawn.
A combination of a special hardware infrastructure and possible operating modes or modes of microcontrollers (μC) such as the so-called subclock mode, are generally used for leaving the quiescent current mode at a defined point in time. The physical bus connection by so-called transceivers, or transmit and receive units, for the currently used procedures includes the step of initiating the wakeup of connected hardware modules and microcontrollers. Furthermore, it is necessary to minimize the current consumption in the quiescent mode so that a start of a vehicle is ensured even after longer periods of inactivity.
The German patent application publication DE 601 26 373 T2 describes a vehicle network which encompasses one or more electronic control unit(s), which is/are able to be operated at low power both in an active state and in a quiescent state, and which can switch from the quiescent state to the active state after receiving a wakeup call, which is transmitted by a control unit provided for this purpose. In the process, said control unit also generates a first message after providing the wakeup signal.
A control system for a motor vehicle is known from the German patent application publication DE 10 2004 007 721 A9. The control system includes a first device which is set up to execute at least one control function in the motor vehicle, and it includes at least one control unit which, if required, may be coupled to a drive, an actuator, a sensor or the like and is suitable for executing a function such as unlocking and/or locking the car doors, the ignition start circuit, a steering wheel lock, vehicle immobilizer and a seat control for adjusting the seat position. The first device and the control device are disposed together for the transmission of signals in a vehicle electrical system made up of at least one bus system, in particular. In addition, a control device which operates in the manner of a central quiescent manager is provided, this control device actuating the control unit, so that the control unit is able to be activated for executing its function.